The present invention relates in general to soundproof materials and structures preferably for use in the medical or construction field and wherever it is necessary to control sound emission or transmission. More particularly, the present invention is directed to an improved soundproof structure that can be made in a relatively thin sheet or various other forms and that is of a composite type consisting of hollow glass microspheres in a curable resin base.
Noise pollution has become an ever increasing problem within recent years. Because of the increasing interest by environmentalists as evidenced by the enactment of both state and federal laws, there is an increased requirement to protect from and/or restrain sound emission. There have been techniques available to achieve sound reduction or confinement, but these techniques have certain limitations or disadvantages associated therewith.
The usual process to obtain improved acoustic attenuation is to increase the thickness of a wall or partition. However, there are disadvantages associated with this practice such as the attendant cost increase, weight increase and massive thickness.
Accordingly, it is an object of the present invention to provide a soundproof material and structure preferably in the form of a panel that can provide good sound attenuation with a relatively thin panel thickness.
Another object of the present invention is to provide a soundproof structure that can be manufactured relatively cheaply and that is characterized by other characteristics such as good insulating and fire resistance qualities.
Regarding the theory relating to the discovery of the present invention, it is known that airborn sound is transmitted by the molecules of the air. It is transmitted through a rigid partition, for example, such as a wall, by forcing the wall into vibration. The vibrating wall or partition becomes a secondary source radiating sound to the side opposite the original source. For most conventional soundproof structures over a large portion of the audio frequency range approximately a 4-5 db loss occurs for each doubling of the weight.
Traditionally, therefore, it has been customary to depend on thickness, density and/or porosity to achieve varying levels of elastic wave attenuation in acoustic materials. It has been recognized in accordance with the present invention that at least two other factors are significant in providing further improvement of sound attenuation in panels and in other materials.
A soundwave tends to set in motion the molecules of a substance that it impinges upon and the material, as a result, moves as a direct function of the impinging wave. It is theorized in accordance with the present invention that the material will absorb varying amounts of energy depending upon its elasticity and the resonant characteristic of the material. It has been found that a material that has a very good low frequency (100-2,000 hertz), mechanical vibration/stock transmission absorbing quality is characterized by corresponding acoustic attenuation performance.
Accordingly, in the present invention the base material that comprises the soundproof structure is preferably a curable resin having a soft flexible characteristic, which correlates to an A or low D scale indentation (Shore) hardness. There are several epoxy resins, polyurethanes, and RTV silicones that have the desired shock/vibration isolation properties, flexure and Shore hardness.
Another factor in accordance with the theory of the present invention relates to the realization that audio frequency soundwaves are very much dependent on the existence of gas molecules for the transmission of sound through air. Thus, in accordance with the present invention the soundproof structure material also comprises a filler material in the form of a myriad of hollow microspheres preferably constructed of glass and which preferably contain at least a partial vacuum which has been found to provide additional improved acoustic attenuation.
Further aspects of the present invention relate to the process by which the structure of the present invention is fabricated. In accordance with this invention it has been further found that by providing at least twice the volume of microspheres to the volume of resin, improved attenuation follows. It is theorized that by providing as large a volume of microspheres as possible that firstly there is a larger vacuum volume and secondly a wave travelling through the material will experience an increased number of transitions between materials of different index of refraction (glass-resin-vacuum).